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  • 1
    Electronic Resource
    Electronic Resource
    Model for discontinuous actuation of ferromagnetic shape memory alloy under stress (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 1295-1301 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ferromagnetic shape memory alloys have demonstrated strains up to 5% resulting from the rearrangement of crystallographic variants by twin boundary motion under an applied field. A model is proposed that describes twin boundaries moving abruptly in order to accommodate either the mechanical energy of an applied stress σε0 or the magnetic interaction energy of the applied field MsH. This model provides predictions of the materials response under both field and load. The principal conclusion of the model is that when one energy, either mechanical or magnetic, becomes larger than the other, the twins will move to abruptly rearrange the entire sample to a variant stable under the new condition. Experiments were performed to verify this model in Ni–Mn–Ga shape memory alloy. The abrupt change of the variant structure was observed experimentally although the twin boundaries only swept through limited potions of the sample. Experimental field-induced strains reached 2.2%. Samples were also tested under cycled field with constant load and showed cyclic strains of 1.5%. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1285867
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  • 2
    Electronic Resource
    Electronic Resource
    Large field induced strain in single crystalline Ni–Mn–Ga ferromagnetic shape memory alloy (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 5774-5776 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A room temperature free shear strain of 5.7% is reported in a single crystal of Ni–Mn–Ga having a composition close to the Heusler alloy Ni2MnGa. A twin boundary was created in a 2 mm×2 mm×25 mm single crystal using a permanent magnet with surface field strength of about 320 000 A/m. A sharp 6.5° bend occurs in the sample at the twin boundary. The surface magnetization changes abruptly across this boundary. By moving the sample relative to the edge of the magnet, we were able to sweep the boundary back and forth along the crystal length. Surface magnetization was measured using a Hall probe and the results confirm that the easy axis is the tetragonal c axis. Powder x-ray diffraction shows that the fcc to body-centered-tetragonal bct martensitic transition of this material involved a 6% reduction of the bct cell c/a ratio, from (square root of 2) to about 1.33. The maximum achievable strain is thus estimated to be 6.2%. The twin planes in the system are the {112}bct and were observed to lie almost normal to the long axis of the sample tested. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372518
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  • 3
    Electronic Resource
    Electronic Resource
    Field-induced strain under load in Ni–Mn–Ga magnetic shape memory materials : The 7th joint MMM-intermag conference on magnetism and magnetic materials (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 7297-7299 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Single-crystal Ni2MnGa shows a nearly 0.2% strain under a magnetic field of 8 kOe at −8 °C. Polycrystalline samples have been prepared near stoichiometry to study the composition dependence of the magnetic and elastic properties. A narrow band of compositions has been found having a range of Curie and martensitic transformation temperatures, Tc and T0, extending to above room temperature. The compressive stress–strain characteristics in variable transverse field were studied in samples selected to have T0 just below room temperature. Stress-induced martensite was observed as expected and the magnetic field was applied under fixed load for various stresses. A transverse field of 3200 Oe caused the sample to strain under load doing work that increased up to 1.3 J/kg with increasing volume fraction of stress-induced martensite. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.367758
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  • 4
    Electronic Resource
    Electronic Resource
    Phenomenology of giant magnetic-field-induced strain in ferromagnetic shape-memory materials (invited) (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 4712-4717 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ferromagnetic shape-memory alloys have recently emerged as a new class of active materials showing very large magnetic-field-induced extensional strains. Recently, a single crystal of a tetragonally distorted Heusler alloy in the NiMnGa system has shown a 5% shear strain at room temperature in a field of 4 kOe. The magnetic and crystallographic aspects of the twin-boundary motion responsible for this effect are described. Ferromagnetic shape-memory alloys strain by virtue of the motion of the boundaries separating adjacent twin variants. The twin-boundary motion is driven by the Zeeman energy difference between the adjacent twins due to their nearly orthogonal magnetic easy axes and large magnetocrystalline anisotropy. The twin boundary constitutes a nearly 90° domain wall. Essentially, twin-boundary motion shorts out the more difficult magnetization rotation process. The field and stress dependence of the strain are reasonably well accounted for by minimization of a simple free energy expression including Zeeman energy, magnetic anisotropy energy, internal elastic energy, and external stress. Models indicate the limits to the magnitude of the field-induced strain and point to the material parameters that make the effect possible. The field-induced strain in ferromagnetic shape-memory alloys is contrasted with the more familiar phenomenon of magnetostriction. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373136
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  • 5
    Electronic Resource
    Electronic Resource
    6% magnetic-field-induced strain by twin-boundary motion in ferromagnetic Ni–Mn–Ga (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 886-888 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Field-induced strains of 6% are reported in ferromagnetic Ni–Mn–Ga martensites at room temperature. The strains are the result of twin boundary motion driven largely by the Zeeman energy difference across the twin boundary. The strain measured parallel to the applied magnetic field is negative in the sample/field geometry used here. The strain saturates in fields of order 400 kA/m and is blocked by a compressive stress of order 2 MPa applied orthogonal to the magnetic field. The strain versus field curves exhibit appreciable hysteresis associated with the motion of the twin boundaries. A simple model accounts quantitatively for the dependence of strain on magnetic field and external stress using as input parameters only measured quantities. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1306635
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  • 6
    Electronic Resource
    Electronic Resource
    Fine needle cytology of palpable head and neck lesions: a comparison of sampling methods with and without suction (1999)
    Oxford, UK : Blackwell Science Ltd
    Cytopathology 10 (1999), S. 0 
    Details
    ISSN: 1365-2303
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Patients attending the ear, nose and throat (ENT) department at St James's University Hospital, Leeds, UK, for evaluation of palpable head and neck lesions have a fine needle cytology (FNC) specimen taken and receive the result at the same out-patient visit. This study was designed to discover if there is a significant difference in the efficiency of the methods with and without suction. The method was chosen randomly on each occasion and the adequacy or otherwise of the specimen was determined taking into account the site and nature of the lesion and the total cellularity of the sample. The level of blood contamination was also compared by each method. When benign and malignant lesions from all sites were analysed together the method with suction produced a significantly higher number of adequate samples than the method without suction. The exception was in the case of samples from lymph node lesions measuring 〈 1 cm, where adequate specimens were only obtained without suction. The non-suction technique was particularly poor at sampling salivary gland lesions in the 1–1.5 cm category. There was no significant difference in the level of blood contamination between the two methods at any site. These results are at variance with most other similar studies and possible reasons for this are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2303.1999.00156.x
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  • 7
    Electronic Resource
    Electronic Resource
    An investigation into the transverse and impact strength of `high strength' denture base acrylic resins (2002)
    Oxford UK : Blackwell Science Ltd.
    Journal of oral rehabilitation 29 (2002), S. 0 
    Details
    ISSN: 1365-2842
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: A range of materials, often marketed as high strength resins is available. These materials are often expensive options to conventional heat-cured acrylic resin. The aim of this study was to investigate transverse and impact strength of five `high strength' acrylic resin denture base materials. A conventional heat-cured acrylic resin was used as a control. Specimens were prepared as specified in the International Standard Organization (ISO 1567: 1988) and British standards for the Testing of Denture Base Resins (BS 2487: 1989) and the British Standard Specification for Orthodontic resins (BS 6747: 1987) for transverse bend and impact testing. The impact strength was measured using a Zwick pendulum impact tester and the transverse bend strength measured using a Lloyds Instruments testing machine. The results showed that Metrocryl Hi, Luctitone 199 and N.D.S. Hi all had an impact strength which was significantly higher than the control. For the modulus of rupture, there was a significant difference between Sledgehammer and the other groups. There was no significant difference between the other groups and the control. For the modulus of elasticity, Sledgehammer produced the highest value followed by the control. The remaining four materials had a modulus of elasticity less than the control.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2842.2002.00830.x
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  • 8
    Electronic Resource
    Electronic Resource
    A calorimetric study of precipitation in commercial aluminium alloy 6061 (1991)
    Springer
    Journal of materials science 10 (1991), S. 323-326 
    Details
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00719697
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